Nanoimprint lithography (NIL) has been proved to be a low-cost, high-throughput patterning technology with sub-10 nm resolution. The pressing of a imprint mold into a deformable resist is a key issue affecting the performance and yield of NIL. The conventional methods include (a) a mechanical press using a pair of parallel plates, and (b) an air cushion press (ACP). Both of these methods have drawbacks. The solid plates can hardly generate uniform imprinting pressure within the imprint area, and they induce unexpected shear, rotation, and shift, degrading the over-alignment precision. The air cushion press can generate much more uniform imprinting pressure, but requires a vacuum/pressure chamber, which significantly increases the complexity of a NIL tool and the difficulty of over-layer alignment. Furthermore, there are issues of liquid flow between the mold and the substrate. Protrusions can block flow of a nanoimprint material, and small holes can prevent a complete filling.
In this invention, we present a new pressing method using electrostatic force between the mold and the substrate instead of mechanical force or fluidic pressure, and present a new method of moving nanoimprint materials between the mold and the substrate, unpinning flowing nanoimprint materials, and filling small holes with nanoimprint materials.
The liquid filling into the nano- and micro-features is anther important issue for nanoimprint lithography (NIL), other lithographic technologies based on liquid-filling, and micro- and nanofluidics. Incomplete filling leads to a poor patterning resolution and fidelity and introduces air bubble defects in the functional device structures.
Two key factors affecting the liquid filling are: (1) the dewetting nature of the plates, which expels the capillary filling of the liquid resists into the nanostructures; and (2) the pinning of the air/liquid interface to the micro- or nano-scale features, which can trap air bubbles and hence result in the incomplete resist filling.
There are two conventional methods for achieving complete fillings: (1) the use a sufficient gauge pressure to overcome the dewetting force, and hence drive the liquid into nanostructures. However, an overly large pressure is not desirable because it may damage the templates and device structures and degrade the overlay alignment accuracy in lithography. (2) Chemically changing the surface energy of the plates to make the surface wetting to the liquid. However, this chemical change may also permanently modify the surface properties and require complicated and high-cost chemical processes. For NIL, the adhesion force between the mold and the cured resists may be unexpectedly increased, and the mold separation becomes very difficult.
We present a novel method for filling the liquid resist and other functional materials into the mold/substrate gap and fine structures by using electrohydrodynamic actions (electrowetting, dielectrophoresis, or electrowetting-on-dielectric).